1. Technical Field
This invention relates to methods of masking holograms and, more particularly, to techniques for eliminating crosstalk in multiple exposure holograms.
2. Discussion
There exists several applications for multiple holographic images formed on a common substrate. One such application would be the formation of a seven-segment alphanumeric display. Each segment of the display could be formed by a separate hologram on a common substrate. Each hologram could be played back individually or collectively by appropriate reconstruction beams during a playback mode in order to form a desired letter or number from the display.
One possible technique for forming multiple exposure holograms is to illuminate different areas on a photosensitive substrate with an object beam while the reference beam illuminates all of the photosensitive material. One disadvantage with this technique is that a noticeable amount of interference or "crosstalk" would be generated during playback. In other words, it is difficult to make one but not the other of the holograms visible during playback. This is believed to be due to the fact that the reference beam encompassed a common area of the photosensitive plate where both object beam images were focused during exposure of the two holograms. Another disadvantage is that during construction of the first holographic image the first exposure of the gel would harden it. Consequently, any subsequent exposures would not have the same efficiency as the first exposure, without considerably boosting exposure times or taking other undesirable measures.